Utility knives are known from EP 0,543,781 (U.S. Pat. No. 5,283,954), German Utility Model 1,711,881, German Utility Model 7,207,013, German Utility Model 94 17 085, and U.S. Pat. Nos. 2,679,100, 3,316,635, 4,139,939, 6,163,963, 6,449,850, and 6,546,632 that have an elongated body formed as a grip or handle and from which can project a replaceable steel blade, typically of right-trapezoidal shape. Such a knife is used for opening packages, numerous construction applications, and in the food industry.
In most such utility knives the blade is mounted on a slide that can shift it between a retracted position with the blade wholly contained in the housing or handle, so that the knife can be pocketed safely, and an extended position with the blade projecting from a front end of the handle, so that the knife can be used. As a rule a button that actuates the slide and that normally is formed as part of the slide is exposed on the back edge or one side of the housing. The provision on the back edge has the advantage that it allows the knife to be used with equal facility by right- and left-handers, but this construction has the disadvantage that the resultant grip, with the thumb on the back of the knife, is frequently not strong enough. Provision of the button on the left side makes the knife difficult to use for left-handers.
The housing is often formed of two separate parts that can be separated to replace the blades, and often also to expose a compartment holding a supply of spare blades. In a standard model, a screw that can be operated by a coin is provided at one end of the housing extending between the housing halves. Thus the screw can be pulled to separate the two housing halves, making blade replacement possible. Such an arrangement has the disadvantage that the screw can easily get lost, making the knife unusable.
When used in the food-services industry, it is essential that the knife by constructed such that it does not have crannies that can hold food particles, leading to cross-contamination of product. In such an application it is desirable to make the knife disposable so that it can be replaced frequently, making the transmission of bacteria impossible.